1. Field of the Invention
The present invention generally relates to a technology for connecting a transmission-side unit having integrated circuits and a reception-side unit having integrated circuits with respective connectors to a backboard, and more specifically relates to canceling a reflected wave that generates in the connectors and gets superimposed on a signal wave.
2. Description of the Related Art
Conventionally, in general, an electronic device is constituted by connecting substrate units mounted with electronic circuits including integrated circuits via a back board. Connectors in which output terminal pins of the substrate units are inserted are arranged on the backboard. When the output terminal pins are inserted in the connectors, the substrate units and the backboard are electrically connected. Communication between the substrate units via the backboard is referred to as backboard transmission.
A repeater of a communication network is explained as an example of the electronic device. According to the increase in traffic, improvement of processing ability of the repeater is attempted. Conventionally, in general, the number of channels of the repeater is increased to improve the processing ability of the repeater. However, when the number of channels is increased, the number of components of the repeater is also increased. As a result, a size of the repeater is increased.
On the other hand, to improve the processing ability without causing the increase in size of the repeater, it is attempted to improve a processing rate of one channel without increasing the number of channels. However, reliability of high-speed communication in the backboard transmission hinders the improvement of a processing rate of a channel.
The substrate units and the backboard are connected by fitting pins in holes called through-holes. However, there are portions where the pins and the through-holes are in contact with each other and portions where the pins and the through-holes are not in contact with each other. Thus, the portions where the pins and the through-holes are not in contact with each other are bypassed in terms of an electric circuit. The portions are called stubs.
In the high-speed communication in the backboard transmission, a delay wave generated in the stubs is superimposed on a direct wave to be noise. A gain of communication signals carried by the direct waves is damaged by this noise. In other words, the noise hinders an increase in speed of the backboard transmission and spoils reliability of the high-speed communication.
To cope with such a problem, for example, a backboard transmission method including connectors for connecting substrate units and a backboard that can prevent stubs from being formed and prevent a delay wave from being generated is disclosed in Mitsubishi Electric Corporation, “Transmission between boards in a repeater at speed of 10 Gbps and a distance of 50 mm was demonstrated for the first time in the world”, [online], Oct. 2, 2003, news release, [retrieved Feb. 1, 2006], Internet URL:http://www.mitsubishielectric.co.jp\news-data/2003/pdf/1002-b.pdf. According to this backboard transmission method, it is possible to prevent noise and a loss of gain of communication signals and secure reliability of the high-speed communication.
However, in the technology represented by the document described above, reliability of high-speed communication at about 10 Gpbs is only secured. The technology is not applicable to high-speed communication at higher speed in recent years. Specifically, in the high-speed communication in the backboard transmission, an influence on reflected waves due to impedance mismatching between the substrate units and the connector sections is a significant problem.
In low-speed communication, the influence of reflected waves occurs in one time slot and the reflected waves affect only a waveform of a pulse of one bit. However, in the high-speed communication, since a time slot is reduced, the reflected waves affect a pulse of a plurality of bits in a plurality of time slots. This makes it impossible to accurately receive the bits of the pulses.
Therefore, there is need of a technology that can eliminate the influence of reflected waves due to impedance mismatching in the connector sections in the backboard transmission at higher speed, accurately receive pulses, and accurately discriminate bits.